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        <td class="header">&nbsp;
            OPeNDAP Client Overview
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<p>
    The OPeNDAP client allows to access an OPeNDAP server and download files using the data access protocol
    (DAP).
    The client offers the possibility to filter the displayed catalog entries by various characteristics before
    downloading.
</p>

<p align="center"><img src="images/opendapclient.png"></p>

<h3>Access to servers</h3>

<p>
    Server access is established by entering the URL of a THREDDS catalog file of an arbitrary OPeNDAP server in the
    "Root URL"-field and typing 'Return' or clicking <img src="images/icons/ViewRefresh22.png">. The catalog content
    will then be displayed
    as a tree structure. The application will remember previously entered URLs.
</p>

<h3>Navigating through the catalog tree</h3>

<p>
    The tree structure on the left displays the contents of the chosen server.
    Files which can be accessed via DAP are displayed as <img src="images/icons/DRsProduct16.png"> .
    For files accessible via DAP, their DDS and DAS are displayed in the information box below the tree. For more
    information about DDS and DAS please refer to http://www.opendap.org/pdf/dap_2_data_model.pdf.<br>
    Multiple files may be selected.
</p>

<h3>Using the filters</h3>

<p>
    The filters allow the user to narrow down the number of displayed files. A filter can be set after selecting the
    respective check box. Note that the filters are not active before the apply button has been clicked.
    The filters will become (in)active again after (de)selecting the check box. Multiple filters may be combined to
    refine the search for files.<br>
</p>

<h4>Using the dataset name filter</h4>

<p>
    Using the dataset name filter a search for whole file names or parts appearing in a file name can be performed.
    It supports the wildcards *, +, and ?'.<br>
    For example, if the entered filter is *2007*, only file names that contain 2007 are listed.<br>
    If the entered filter is *b+*, only file names containing at least one b in their file name.<br>
    If the entered filter is *.dima?p?, all file names with the extensions dim and dimap are listed.
</p>

<h4>Using the time range filter</h4>

<p>
    The time range filter can perform a temporal restriction on the files files of the selected server.<br>
    If the chosen OPeNDAP-server provides time coverage information for its files, these information are used. If not,
    the filtering is performed using the file name. In the latter case both the date pattern and the filename pattern
    need to be provided by the user.<br>
    For example, the filename '<i>MER_RR__2PPBCM20080208_230550_000002002065_00451_31066_0001.N1</i>' employs the
    date pattern <i>yyyyMMdd_hhmmss</i> and features a start time, so that the filename pattern <i>*CM${startDate}_*</i>
    should be used. The filename '<i>sst_northsea_20010101_20010201.nc</i>' employs the date pattern <i>yyyyMMdd</i>
    and features both start and stop time, so the filename pattern <i>*_${startDate}_${endDate}*</i> should be used.
</p>

<p>
    Common pitfalls when using the time range filter:
<ul>
    <li>
        If the date pattern matches multiple parts of the filename, the last match is considered the date. Thus, to
        safely use the filter for the file '<i>sst_northsea_20090102_61504254.nc</i>',
        the filename pattern '<i>*${startDate}*</i>' is
        not sufficient; in this case, the more specific filename pattern '<i>*_${startDate}_*</i>' should be used.
    </li>
    <li>
        For the same reason it is advisable to provide the patterns as precisely as possible. If for example a file
        '<i>sst_northsea_20090102_100410_000000992075.nc</i>' shall be filtered, both the date patterns
        <i>yyyyMMdd</i> and <i>yyyyMMdd_hhmmss</i> are potentially correct, but while the former matches two parts
        of the filename and therefore yields wrong results, the latter is unique.
    </li>
</ul>
</p>

<p>
    Setting only a start time will filter out all files before the given time, setting only an end time will filter out
    all files after the given time, and setting both start and end time will filter out all files not completely within
    the resulting temporal range.<br>

    Files that carry no temporal information will not be filtered out.
</p>

<h4>Using the region filter</h4>

<p>
    The region filter filters out all products that do not intersect the chosen geographic region.
    This filter relies on information about the files' geospatial extents.<br>

    If the OPeNDAP server does not provide geospatial information about a specific file, that file will not be affected
    by
    the filter.
</p>

<h4>Using the variable filter</h4>

<p>
    The variable filter filters out products that do not contain certain variables.
    Initially, no information about variables are available, so the filter will start scanning for variable information
    when browsing through the catalog. It is applicable as soon as variable information are available.<br>
    When applied, the filter will keep all files which contain at least one of the selected variables.
</p>

<h4>Downloading files</h4>

<p>
    The selected files are downloaded by clicking the "Download" button.
    When the client is run in the Sentinel Toolbox, the products can be opened immediately after their download is
    complete.
</p>

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